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Investigating forensics

Investigating forensics


 Resources / Archaeology

Forensic Archaeology

Forensic archaeology is the application of archaeology (the study of past cultures and activities) to legal investigations. The skills and methods used by archaeologists to find and interpret buried or hidden sites of past activity have direct application to modern forensic investigations. In North America, forensic archaeology is often considered to be a specialization of forensic anthropology.

In the 1970s and 1980s, criminal investigators began to call upon archaeologists to help locate, excavate and document certain types of crime-scene evidence - usually clandestine burials  of murder victims. Over the next couple of decades, archaeologists became more actively involved in different types of investigations including the excavation of mass burials of victims of modern wars and the recording and recovery of mass fatality events. The main tasks that a forensic archaeologist assists with are: Evidence searches, evidence recovery, evidence recording and scene interpretation.

Evidence search

The search for evidence begins when an object or information leads investigators to believe that a crime or suspicious death has occurred. A forensic archaeologist is typically called when human remains are found scattered on the ground surface and/or remains are suspected to be buried. The first task of a search is to define the area of investigation. This task is usually performed by the archaeologist working alongside the authorities such as the Coroner and Police. The Coroner and Police may have witness testimony that triggers the investigation. The archaeologist will examine a potential crime-scene identified by the witness and try to determine if their testimony is true or not. 

In most instances, human remains are found on the surface. Archaeologists are accustomed to conducting "surface surveys", whereby they inspect the ground surface recording and collecting evidence of past human behaviour. In a forensic context, such evidence occurs when a person has died or been killed outside and the natural processes of decomposition and scavenging by animals and insects affects the position of the body or body parts. Scavengers competing for food can drag body parts kilometres away from their original location. Rain, gravity and other natural processes can also change the location and condition of remains as well as associated objects such as the contents of a person's pockets. Archaeologists have experience in locating evidence and reconstructing the original scene and position of the body through an understanding of these natural processes.

When a body is buried, there are several changes that occur to an area that can generally be detected by the forensic archaeologist. One of these is the change of soil compaction: Soil is made up of organic and mineral components that form through natural processes. Soil typically forms over very long periods. People affect the natural soil when, for instance, they plough it to plant crops, or cut into it to construct buildings. When people interrupt naturally formed soil, they change how solid it is (its compaction). The same principle applies when a person digs a grave to bury a body. Loose, less compact soil suggests that it has been recently disturbed, typically by human or animal activity. Sometimes contrasts in soil compaction can be seen but archaeologists using tools such as a shovel or trowel can usually feel the difference in soil compaction, which tells them where the naturally formed soil has been disturbed.

Soil compaction changes with the size of the soil grain. Sand grains are larger than silt grains, which are in turn larger than grains of clay. Soil compaction can naturally differ greatly from one area to another, but recent clandestine or unmarked graves show soil looser than the naturally formed soil that surrounds them. The same principles apply for more ancient archaeological features and activity, but over time the compaction of the disturbed soil generally appears more like the undisturbed soil around it.

Disturbed soil looks different

In the images above, contrasts in soil can be seen between the darker-coloured, looser soil that is filling a grave and the lighter, more compact soil that has not be disturbed.

Other changes that occur during the burial of a body, which might be detectable by a forensic archaeologist, include the creation of a small mound as a result of filling in soil on top of a body; sometimes some of the soil that was placed at the side of the grave during its creation is left there, and this covers vegetation and also makes the area slightly mounded; over time the soil over the body in a grave compacts and lowers, especially over the torso of the body when the organs decompose and the rib cage collapses; different plants take advantage of looser soil and greater levels of moisture (although decomposition fluids from the body can also be toxic to plants). Generally, the area of a burial is composed of looser, darker, more organic soil than that which surrounds it. All of these features help an archaeologist identify a potential burial and indicate the area that should be excavated to locate buried evidence such as a body.

Evidence recovery

Most forensic archaeological investigations take place outdoors, where considerations of scene location and weather must be made. One must make carefully consider logistics  to determine what equipment is necessary and potentially useful. A consideration of logistics also implies planning for broader issues such as how to approach the site and how to delimit the area under investigation.

In the case of buried evidence, a forensic archaeologist will excavate. Excavation refers to the process of digging out or uncovering objects in the ground. In a forensic investigation, an archaeologist may be called to excavate a grave. Before the destructive process of excavating a grave begins, all evidence on the ground surface must be documented and collected. Surface evidence can include plants, insects, objects such as clothing or a weapon, and human remains. All evidence should be photographed and mapped, showing the location of each item in relation to other evidence as well as to other important features such as buildings, streams, roads or fences. Once the location of evidence is documented, investigators may collect it. How each piece of evidence is collected and cared for depends on various factors, explained in the section: Inventory of Evidence.

Excavation is destructive, so careful documentation of the work is very important. At a scene with a grave, the forensic archaeologist's first task is to define the shape and size of the grave. Then, they remove the soil inside the grave carefully - documenting, photographing and collecting everything that is found that might help understand how that person died, was buried and who they are. Excavated soil is often screened  to look for small objects, bones, insects or other evidence that can help with the investigation.

There are many types of equipment that help recover and analyze evidence from a crime scene. Mapping the area and evidence may involve a GPS (global positioning system), a compass, a level, a plumb bob, pencils, scale rulers, graph paper, measuring tapes and string for creating a grid over the scene. More advanced survey equipment may include a "total station", which measures distances in three dimensions using lasers and a prism held over the object being mapped.

Excavation typically involves the use of a shovel and small trowel. Soft wooden or plastic tools should be used around the body so as not to scratch or damage bone. Gloves should always be worn to protect hands from sharp or other dangerous objects in the search area. Likewise, investigators usually wear masks and body suits to protect both the evidence and themselves from contamination. With larger operations like mass grave  excavations, driver-operated mechanical excavators such as back-hoes are typically used to begin the search for or excavation of buried evidence.

Since human bone can be fragile, forensic archaeologists and anthropologists must also ensure they have the right supplies to recover and handle the remains. Skeletal evidence is usually placed in paper bags and then put in acid-free boxes to help protect them while being transported for analysis. Paper bags are used because they absorb the moisture and help prevent the formation of mould or other fungi.

When an excavator reaches the body in the grave, they draw and photograph the remains before removing them. Excavation continues until the whole grave is exposed and emptied.  The purpose of an excavation is not only to recover the human remains, but also any other objects or information that might explain who the individual is and what happened to them.

Evidence recording

Sometimes the evidence uncovered by forensic archaeological investigation will be used in court trials. In some countries such as Canada, judges, juries and lawyers are not at a crime scene during an investigation. They do not know what the scene looked like when it was discovered. In addition, the investigation itself changes the scene:  investigators disrupt the scene by walking across it, digging and collecting evidence. For these reasons, it is extremely important to record the scene as it appeared when discovered and analyzed. Details about the location and condition of evidence must be recorded at the time and place of discovery, or "in situ ".

Investigators may use grid squares to record and map a scene and show the location of all evidence found there. They make a grid of evenly-sized squares across the site with stakes and string. Typically, each square in the grid will be 1 metre by 1 metre, although this may change according to the investigation's needs. Investigators usually mark one axis of the grid with letters and the other with numbers, so that each square has its own name like A3 or D6. Grids should begin with the marking of a single point called a datum.

Creating a grid  is very useful if investigators are digging at a scene, because they must remove evidence found on the surface before digging. Recording spatial relationships in three dimensions lets them detect associations. For example, the shell casing from a gun might be found on the surface of grid square 1A and a grave located beneath the surface in the bordering square 2A. The closeness of the locations suggests that the casing and grave are related.

Mapping a scene - drawing it on paper or using digital technology - is an important method of recording the area and the evidence discovered. A map can be used with other recording methods like photography to demonstrate what was found at a scene and where it was found. A good map includes the name of its creator, the date, the name or code of the scene, an arrow that indicates north, and a scale. The scale shows how much smaller the map is than the real scene. For example, a 1:100 scale means that one centimetre on the map represents 100 centimetres at the scene. A problem with paper maps is that they are two-dimensional (length and width) representations of a three-dimensional scene (length, width and depth). As a result, multiple maps may be needed to show different vertical levels. For example, one map will show a bed in the room, and another will show the position of evidence found and collected from under the bed. Profile maps can also be created, which show things from a 'side' view, rather than the more common aerial view.

An example of a map

Mapping a scene, the surrounding area and the location of all the evidence is an important part of recovery and crime scene work.  Triangulation is one method of measuring the relative distance between objects. Triangulation works by setting up a base line, a line that crosses the scene and from which measurements are taken. The position of the base line should be related to the datum. All evidence and features of the scene can then be mapped from two different points along the baseline forming a 'triangle' of measurement with the object being mapped. In this way, one can create a scale map with distances of all objects recorded relative to the baseline and to each other. Triangulation can provide a simple alternative to creating a grid square. If a scene is very large, investigators may use a combination of both methods by creating a very large grid of, say, 10 x 10 metre squares, and then triangulating objects from the two corners of any given square within the grid.

Scene and evidence interpretation

Documenting a scene is important, but attempting to explain why and how things came to be is a critical contribution that archaeologists can make to forensic investigation. Forensic archaeological interpretation focuses on several key areas: context; association; provenience; time elapsed since deposition; and site/scene formation.

Context. A central concept in archaeology that is used in crime-scene interpretation is context. Investigators consider objects or people discovered during a forensic investigation in relation to other objects and people found nearby. These other areas and objects make up the context. Investigators think about context to see how an environment affects or relates to an object. If a bone is found on a farm, the context suggests that the bone is probably from an animal. If the bone has cut marks and the investigator knows that animals are butchered on the farm, the cut marks have a logical, non- criminal explanation.

But the most obvious or logical explanation is not always correct.  A skull at the bottom of a steep slope suggests that it rolled down the slope after decomposition and the skull's separation from the body.  But the person may also have died elsewhere and a scavenger dragged the skull to the discovery site, using the slope as cover from competing scavengers. Understanding the context - the area and objects around something of forensic interest - help investigators explain what it is, what it is related to, how it came to be in that place and why it is important to an investigation.

Association. Associations are relationships or connections between objects, places or people that can help forensic investigators solve cases. For example, a bullet that injured a victim can be connected to a shell casing found nearby the place of the shooting. That shell casing can be matched to a particular gun, the owner of which may have been the shooter. The shell casing, the bullet, the gun, the victim and the offender are all associated with each other.

An unidentified body's location can give clues through an association with a type of person that frequents that place. For example, a body on a remote, unmarked trail suggests that the person was a hiker or hunter who knew of and used the trail.  But associations can be misleading: the deceased could also have been a lost tourist who came upon the trail by chance. Forensic investigators should consider all possible associations but not eliminate any other possibilities.

ILLUSTRATION: mass grave with four people in a row and a watch with a broken band next to the wrist of the first person but between first and second person.

Provenience. Trying to establish provenience is an important part of archaeological interpretation. Provenience, also sometimes called "provenance", refers to the place from which an object came, as opposed to where it was found. In forensic investigations, bodies or body parts are often found on the shore of a river or other body of water. Often the body started somewhere else and washed up at the point of discovery. Provenience of the body refers to where it came from, usually meaning where the person died and, in this case, first came to be in the water. Different factors can affect the movement of the body such as water currents, the body's buoyancy from clothing or a life vest, or scavenging by marine animals. Investigators must consider these factors carefully when establishing the body's provenience. Correctly identifying these variables and finding the body's provenience can be critical to establishing who the person was, how they came to be in the water, how and when they died. Similarly, a running shoe with a human foot might be found on a beach. Pollen and soil grains from the tread of the shoe may indicate the provenience of the person by showing the environment in which they were walking before the body entered the water.

Time elapsed since deposition. In a forensic context, establishing how long evidence has been at a scene is an important challenge. Typically, time elapsed since deposition relates directly to the post-mortem interval (also "Time Since Death"). As archaeologists are accustomed to analyzing evidence that may be very old, they must consider how the condition of the evidence at the time of discovery might be different from the original condition when the evidence was first deposited. In the case of human remains the archaeologist must consider decay rates of soft tissue (e.g., muscle and skin) and scavenging relative to temperature, humidity, altitude, the type and number of local scavengers and local plants, whether or not remains were buried, and if so, the effects of soil acidity. As there are so many factors involved, post-mortem interval estimates are seldom precise (e.g., a time since death estimate may be a range of one week to three months), but every piece of new information can help identify a victim and establish how they died.

Site/scene formation. This is the process by which a crime scene is created, the result of interaction between people and a place. Site formation can be the result of intentional acts like digging a grave, or unintentional acts like leaving footprints. Crime scene investigators analyze the scene to try to understand the events that formed it. They do this by photographing and drawing the scene as discovered, then collecting physical evidence. After that, they use logical, critical thinking to establish how the scene was affected by the people who were there.

Knowing if a burial was intentional can be important in deciding if a crime was committed or if the death was an accident. For example, careful excavation of a buried body may demonstrate if the body was buried by natural or unnatural processes. The natural explanation could be that the body was in a river that flooded over its banks. The body, bloated during the decomposition process, could float into a low-lying area. As the body decomposes and skeletonizes it will sink. Rushing water can move silt and sand into the area over time and cover up the skeleton. As the water level drops, the skeleton can be partially or completely buried. The unnatural burial will occur when a person digs a hole and places a body into it before filling the hole back in with soil. The natural explanation may be the result of a person drowning in the river, whereas the unnatural burial is more likely related to a crime.

Report writing

A report is a formal description of an event or investigation. A forensic report explains what an investigator did, how they did it and what they think the evidence shows.  A forensic investigator's report is especially important because it must be able to explain the results of the investigation to a judge and possibly a jury who would not be able to attend a crime scene and observe an investigation first-hand. There are no agreed-upon protocols or standards for writing forensic reports in Canada, but most forensic scientists use a scientific format that includes the following:

  • Report summary
  • Background (how the author became involved in the case)
  • Qualifications of the author (what makes the author an authority on the subject)
  • Materials, methods and limitations (what work was done, how and why it was conducted, and any barriers to further investigation/analysis)
  • Results (what the evidence found)
  • Interpretation of results (what the evidence means, within the area of expertise)
  • Conclusions (another short summary of the case, the findings and their importance)
  • Bibliography (what sources of information - professional literature, interviews etc - were used).